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According to Commodore: The Amiga Years, the reason the Commodore UNIX machine project in the early 80s used the Z8000 rather than the 68000 was an ongoing lawsuit with Motorola:

With the Commodore-Motorola lawsuit over the 6500 line of microprocessors still ongoing, the plan remained to use the 16-bit chip from Zilog.

What was this lawsuit about? I know there was one in the early days of MOS Technology over the 6501 being a drop-in competitor to the 6800, but I thought this was resolved back in the mid-70s?

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The only issue that comes to mind was the original Motorola vs. MOS case about the 6501 being pin compatible to the 6800. Since MOS was by then part of Commodore, their settlement not to make a compatible CPU might be referenced here, as this was of course future binding.

But as the wording already suggests, the decision might be more based on a bias than real legal implications. Also consider that the Z8000 was anyway a rather good choice for a 16 Bit Unixoide system, which leaves lot of room to foster some grudge.

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    Oops yes, 6501. I don't know enough about the Z8000 to have an opinion on whether it was a good choice, but I found it interesting that the people who were there at the time, thought it was not; they said they would have preferred the 68000, had corporate politics not dictated otherwise. – rwallace Sep 9 '18 at 20:35
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    The weird thing, from the start, is that the 6501 wasn't compatible in any way other than the pins. It was ridiculous, and any other company would have laughed them off. – Maury Markowitz Sep 9 '18 at 21:12
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    @MauryMarkowitz Not realy ridiculous, as it was an attack into the heart of Motorolas business. While 6800 CPU and 6820 PIA where in production rather similar, the CPU did sell for several times of the PIA. MOS' business idea was to undercut motorola with the 6501 by large and at the same time benefit from the many perhipheral chips Motorola had already designed, saving that upfront investment. The 6502 ff where ment as versions to work with the intended 653x all in one chips for extreme low cost. – Raffzahn Sep 9 '18 at 22:01
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    Good answer. I wrote an answer intended to affirm the pin-compatibility issue, but I got so anecdotal about the compatibility and tangential matters that I received a well-earned a deletion. The pin-compatibility was remarkable, including operating in an asynchronous clock environment. – cmm Sep 12 '18 at 20:08

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